This invention generally relates to slider-operated flexible zippers for use in reclosable pouches, bags or other packages of the type in which perishable material, such as foodstuff, may be stored.
Reclosable fastener assemblies are useful for sealing thermoplastic pouches or bags. Such fastener assemblies often include a plastic zipper and a slider. Typically, the plastic zippers include a pair of interlockable fastener elements, or profiles, that form a closure. As the slider moves across the profiles, the profiles are opened or closed. The profiles in plastic zippers can take on various configurations, e.g. interlocking rib and groove elements having so-called male and female profiles, interlocking alternating hook-shaped closure elements, etc.
Conventional slider-operated zipper assemblies typically comprise a plastic zipper having two interlocking profiles and a slider for opening and closing the zipper. In one type of slider-operated zipper assembly, the slider straddles the zipper and has a separating finger at one end that is inserted between the profiles to force them apart as the slider is moved along the zipper in an opening direction. The other end of the slider is sufficiently narrow to force the profiles into engagement and close the zipper when the slider is moved along the zipper in a closing direction.
Other types of slider-operated zipper assemblies avoid the use of a separating finger. For example, U.S. Pat. No. 5,809,621 discloses a slider-operated zipper assembly wherein one zipper profile has a pair of handles that cooperate with the slider. As the slider is moved in an opening direction, the handles are squeezed together to disengage the profiles. In U.S. Pat. No. 5,442,838, a slider-operated zipper assembly is disclosed wherein the zipper profiles are engaged and disengaged in the course of a so-called “rolling action”. This “rolling action” is described as being achieved through cooperation between flanges on the profiles and shoulders that project inwardly from the arms of the slider. U.S. Pat. No. 6,047,450 discloses a zipper comprising a pair of mutually interlockable profiled structures. The first profiled structure comprises an interlocking element on a surface directed toward the second profiled structure and an integral base directed away from the second profiled structure. Likewise, the second profiled structure comprises an interlocking element on a surface directed toward the first profiled structure and an integral base directed away from the first profiled structure. Additionally, portions of the two profiled structures form a fulcrum about which the profiled structures may be pivoted out of engagement when lower edges of the bases are forced towards each other.
One of the important features of such reclosable fastener assemblies are the end stops, which prevent the slider from falling off the end of the fastener when the slider reaches the end of the fastener. End stops have taken on various configurations, such as, for example, riveted end clamps such as those described in U.S. Pat. Nos. 5,067,208 and 5,161,286; transverse end stops made from molten material of the fastener strips, as described in U.S. Pat. No. 5,088,971; reciprocating anvils, as described in U.S. Pat. No. 5,131,121; tubular end stops, as described in U.S. Pat. No. 5,405,478; a window structure combined with sealed zipper ends, as described in U.S. Pat. No. 5,442,837; or plastic end clips fused to the zipper as described in U.S. Pat. No. 5,448,807.
U.S. Pat. No. 5,950,285 discloses a reclosable bag having end stops that prevent a slider from moving beyond the end of the zipper when the slider reaches either the closed or fully open position. The end stops are formed from the material of the zipper profiles and “rise vertically” from the zipper to block and prevent further movement of the slider. The end stops are formed by first aligning together the opposing profiles at an end stop area proximate to an end of the bag, and then fusing the zipper profiles at the end stop area to provide a vertical structure for preventing movement of the slider past the ends of the zipper, while at the same time keeping the rails intact. Preferably, the profiles are fused by directing ultrasonic energy to the end stop area. Optionally, the end stops have ridges disposed along their surfaces.
In addition, U.S. Pat. No. 6,357,914 discloses a slider-operated zipper in which the ends of the zipper profiles are deformed or “crushed” to form slider end stops. Preferably, the slider end stops are formed by the application of ultrasonically generated heat and pressure to the ends of the zipper profiles. The sides of the zipper profiles are softened and compressed at end stop areas so as to impart a pre-selected width and an upwelling displacement above the uppermost surfaces of the zipper profiles. The material displaced above the upper surface of the zipper profiles interferes with the top wall and ends of the slider to limit its sideways travel along the zipper. The slider end stops (that is, the deformed portions of the zipper profiles) are configured to avoid deformation of the bottom surfaces of the zipper profiles. The lower ends of the zipper profiles extend undeformed substantially to the side edges of the package. The end stops and the undeformed bottom surfaces of the zipper profiles in the area of end stops cooperate to hold the slider, preventing the slider from being unintentionally derailed. The '914 patent asserts that separation of the “crushing” operation performed on the zipper profiles to form the slider end stops from the conduction heat sealing operation to form the side seals allows the end stops to be reduced in size, effectively extending the size of the package opening without sacrificing the ability of the end stops to effectively retain the slider on the zipper.
There is a need for a method and an apparatus for ultrasonically deforming the ends of a slider-operated zipper to form structures capable of stopping a slider from sliding off an end of the zipper when incorporated in reclosable packaging.